Phospholipase D characterizes a group of enzymes which transfer a phosphatidic acid moiety from an acid or an alcohol to an alcohol or water. The activity is found, for example, in vegetables, such as carrots and cabbage. The enzyme species found in cabbage is widely studied and has been denoted as phosphatidylcholine phosphatidohydrolase (Enzyme Commission No. 3.1.4.4). This enzyme hydrolyzes phosphatidylcholine into phosphatidic acid and choline. This enzyme has been assayed by using radiolabeled phosphatidylcholine or by using coupled enzyme assays which detect the product choline. These assays are complicated and/or difficult.
Phospholipase C characterizes a group of enzymes which transfer phosphate monoester from a donor alcohol to an acceptor alcohol or water, where diacylglycerol is either the donor or the acceptor group. A species of the enzyme is recognized to have important physiological significance in coupling a hormone binding event outside a cell whereby diacylglycerol is freed to transmit a signal to activate a metabolic response inside the cell. The phospholipase C activity of phosphatidylcholine cholinephosphohydrolase has been assayed using a p-nitrophenylphosphorylchcline (pNPPC) as a chromogenic substrate. The disadvantage cf pNPPC is that its cleavage is not specific to lipases which have been defined as esterases which act at oil-water interfaces by P. Desnuelle in Advances in Enzymology (1961), Vol. 21, pp. 129-161.